1. Field of the Invention
The invention relates to an image forming apparatus for forming an image by the use of an electrophotographic printing method, an electrostatic recording method or the like, and particularly to an image forming apparatus such as a copying machine, a printer or a facsimile apparatus.
2. Description of Related Art
As an example of an image forming apparatus for forming an image by an electrophotographic printing method, such as a copying machine or a laser beam printer, there is a full-color image forming apparatus adapted to form an image by superimposing Y(yellow), M(magenta), C(cyan) and Bk(black) color component images one upon another.
A color image by color toners formed in the manner described above has its surface smoothed when it is heated and fixed by a fixing apparatus and therefore, has glossiness differing from that of the surface of paper. Therefore, the glossiness of an image portion by the toners is high and the glossiness of a non-image portion is low and thus, it is difficult to uniformize the glossiness on a recording material.
So, as a technique of suppressing such a difference in glossiness between the image portion and the non-image portion, there has been proposed a method of using transparent toners besides the above-mentioned color toners (Japanese Patent Application Laid-open No. S63-58374, Japanese Patent Application Laid-open No. H04-278967, Japanese Patent Application Laid-open No. H04-204670, Japanese Patent Application Laid-open No. H05-232840 and Japanese Patent Application Laid-open No. H07-72696). Specifically, it attempts to form a transparent toner image on the non-image portion to thereby reduce the difference in glossiness from the image portion.
However, the temperature of a fixing roller becomes different between the fixing roller immediately before the heat thereof is taken away by a recording material and the fixing roller immediately after the heat thereof has been taken away by the recording material, and there is the possibility that a faulty image may occur due to such a temperature fall. Specifically, in the first round (hereinafter referred to as the first revolution) wherein the fixing roller contacts with the recording material (the first sheet in a job wherein image formation is continuously effected on a plurality of recording materials), the fixing roller is not in contact with the recording material immediately before and therefore, there is no temperature fall, but in the next round (hereinafter referred to as the second revolution) of the fixing roller, a temperature fall occurs due to the recording material. That is, a difference occurs between the fixing capability of the fixing roller in the first revolution thereof and the fixing capability of the fixing roller in the second revolution (and subsequent revolution) thereof, and there has been the possibility that a faulty image may occur due to this. As the result, glossiness becomes high if the fixing temperature is high, and conversely glossiness becomes low if the fixing temperature is low and thus, uneven glossiness occurs to an image.
In the apparatuses described in the above-mentioned publications, a transparent toner image is not formed with the above-described reduction in the fixing capability from the first revolution of the fixing roller to the second revolution (and subsequent revolutions) thereof taken into account and therefore, there is the possibility of uneven gloss occurring to the image. That is, the image formed on the recording material assumes a state in which a portion of high glossiness and a portion of low glossiness are mixedly present, there is the possibility of the quality of image being lowered.